Protein Synthesis and Codons Practice Protein synthesis is the process where a sequence of DNA is used to build a protein from individual amino acids. The first step in this process is called TRANSCRIPTION, where a coding region of DNA is converted to messenger RNA (mRNA). During transcription, mRNA is made from the DNA sequence following the base pair rule, except RNA does not contain the base Thymine, but instead has Uracil. The mRNA then leaves the nucleus and goes to a ribosome in the cell's cytoplasm. The ribosome reads the message three bases at a time, called a CODON. Each codon will specify a single amino acid. The amino acids are joined together and folded into a protein, a process called TRANSLATION Key Points ● ● ● ● ● ● DNA is used to make a copy of mRNA (transcription) mRNA leaves the nucleus and goes to ribosomes 3 bases = codon 1 codon = a single amino acid A chain of amino acids = a protein Protein synthesis is also called translation Biologists use a codon chart or a codon wheel to determine the amino acids. Amino acids are usually abbreviated on these charts as three letter words, like Cys and Ser. 1. Use the codon chart to write the amino acid that corresponds to each codon found in mRNA: Pro C C C ______________________ C A G GLn ______________________ Ser A G U ______________________ Tyr U A C ______________________ Glu G A A ______________________ Arg C G U ______________________ Phe U U U ______________________ Pro C C A ______________________ 2. Write the CODON that corresponds with each amino acid. There may be more than one. The full names are written, but the codon chart only shows the first three letters. CCA, CCU,CCG,CCC proline ______________________ GGT, GGC, GGA, GGG g  lycine ______________________ GUC, GUA, GUG valine GUU, ______________________ TTC p  henylalanine TTT, ______________________ GAC histidine CAU, ______________________ a  rginine ______________________ CGT, CGC, CGA, CGG, AGA, AGG 3. A single codon is used to signal the beginning of protein synthesis. It is commonly called the START CODON. Locate the start codon on the chart. What are the three bases of this codon? AUG ________ 4. There are three codons that signal the end of synthesis, these are called STOP codons. What are the three stop codons? UGA ________________________________ 5. For each sequence of DNA is shown. Write the complementary RNA sequence underneath the letters, then use the codon chart to determine the amino acid sequence: DNA →  T A C C A T G G A A T T RNA → A U G G U A C C U A Amino Acids → Start condon/Methionine T T C valine U stop condon stop codon C T A G G G A A T G G T RNA → A A G U C Amino Acids → DNA →  Lys Leu A C A RNA → U Amino Acids → Cys G A U A Lys A C A G A U Pro T T T A U G A proline DNA →  U A A C T Asp C A G G U Vla C Trp G C C Pro A C C U C G G T C C A G Gim